1. Field of the Invention
The present invention relates to an apparatus for positioning and locating a baffle plate which is floated in the interior of a crucible when pulling a single crystal.
2. Description of the Prior Art
In growing a single crystal of silicon (Si) or a compound semiconductor of Groups III-V, especially gallium arsenide (GaAs) or gallium phosphide (GaP), from a feed melt contained in a crucible, it is known to float a heat convection preventing baffle plate in the feed melt for preventing a natural heat convection occurring which causes a heat distortion.
It has been proposed in the art to float a baffle plate in a predetermined position below the surface of a feed melt solely by virtue of its buoyancy, but in such case the floating position is unstable and, as the level of the feed melt lowers with growth of a single crystal, holding the baffle plate in the appropriate predetermined position becomes difficult.
It has also been proposed in the art to fix a single control rod to a baffle plate to move and reposition the baffle plate as the liquid melt level lowers with cyrstal growth. In the case, however, for pulling of a single crystal, since the fixing position must be spaced from the center of the baffle plate, the baffle plate may be bent or inclined in use, and thus, a very unstable condition results.
On the other hand, when pulling single crystals of compound semiconductors of Groups III-V typified by GaAs and GaP melting as high as 1238.degree. C. and 1470.degree. C. and exhibiting dissociation pressures as high as about 1 atm and 30 atm, respectively, there has been developed a technique in which the upper surface of a feed melt is covered with a liquid sealing agent such as B.sub.2 O.sub.3, and the interior of the furnace is placed under an inert gas atmosphere of an extremely high pressure of from several tens to several hundreds atm. In such circumstances, if the drive force transmitting means for a baffle plate control rod is sealed against the furnace pressure by a conventional sealing means using a mere sealing material, the sealing material will expand due to the high pressure in the furnace, thus making it impossible to effect a smooth transmission of the drive force and to maintain the furnace interior gas-tight completely.
Also, when using plural control rods, the baffle plate will be inclined or bent unless all the control rods are moved up and down at the same rate. Thus, the technical problem of how efficiently to design a control rod driving mechanism and how to mount same in a limited space so as not to obstruct other devices remains unsolved by the art and the need for a solution still exists.
Further, if one attempts to use a single crystal pulling shaft as the drive source for the baffle, the growth of the crystal will be badly influenced by any vibrations which may occur during transmission of the drive force and the risk is not worth what little may be accomplished. In short, there has to be a better way.